As shown in FIG. 1, for a communications network 100, a path is defined as all physical links 101 and nodes 102 that connect two terminals 110–111. The nodes can be routers, bridges, gateways, and the like The transmission medium of the communication network 100 can be, for example, cable, fiber, wired, wireless, satellite, and the like. The terminals 110–111 can be any type of device capable of transmitting or receiving data via the network 100. For example, in a cable network, the terminal 110 can be a content or Web server, and the terminal 111 can be a television connected to the network via a set-top box. In a wireless network, the terminals can be telephones, computers, PDA's, etc. Depending on the application, a terminal, at any one time, can be source or a destination for communicated signals, or both.
The conventional approach for selecting a path first selects a network, and then selects a path in the selected network on the basis of some desired cost or “objective.” The objective can be attained by evaluating some predetermined objective function. The objective function can consider multiple factors, such as, monetary cost, bandwidth, capacity, link utilization, quality of serve (QoS), and the like. Some factors may be minimized, while others are maximized. For example, some users want to maximize bandwidth and QoS, no matter what the cost, while others may be interested in minimizing cost, even if performance is degraded.
In any case, the objective function is evaluated once, and an optimal path that best satisfies the objective function is selected, and a connection is established. The selected network and path are then used for all access by the terminals for the lifetime of the connection, i.e., a session providing data access services. In FIG. 1, this path is shown bolded. In other words, the selection of the path is static and for a single network.
A variety of methods for selecting the optimal path are known, see for example, R. Bhandri, “Algorithms for Diverse Routing,” Kluwer Academic Publishers, 1999, D. Bertsakas, “Linear Network Optimization: The Algorithm and the Codes,” MIT press, 1991, U.S. Pat. No. 6,301,244, “QoS-oriented one-to-all route selection method for communication networks,” issued to Huang, et al. on Oct. 9, 2001, and U.S. Pat. No. 6,104,701, “Method and system for performing a least cost routing function for data communications between end users in a multi-network environment,” issued to Avargues, et al. on Aug. 15, 2000.
Among the most popular methods are the well-known Dijkstra algorithm, the breath-first-search (BPF) shortest path algorithm, and the Belman-Ford algorithm. These methods basically operate on the same principle. The selection of the optimal path is based on the combined costs of the individual links that form the path.
For instance, the Dijkstra's algorithm models the objective function as a graph with weighted links. Given a root vertex as its input, the function returns, as its output, a label for each vertex on the graph. In the case where the weights represent the length of the links, each vertex label represents the length of the shortest path from the root vertex to a particular vertex. Thus, the algorithm finds the shortest path for traveling from a given vertex on a graph to every other vertex.
U.S. Pat. No. 6,343,122, “Method and apparatus for routing traffic in a circuit-switched network,” issued to Andersson on Jan. and an apparatus for routing traffic in a circuit switched network. This patent relates to traffic switching in a single telecommunications network including a plurality of routes between a call originating and destination terminals with no concern of time variant cost parameters, but not to that in a system with multiple networks with the concern of time variant objectives for use in communication switching. The method includes offering a call between an origin node and a destination node to a preferred route between the nodes, and if the preferred route is not available, offering an alternative route via an intermediate node, and for links between two nodes, setting a first trunk reservation threshold for reserving a certain number of circuits for direct calls along the links between the two nodes, and setting a second trunk reservation threshold for calls between nodes connecting a second link of the alternative route.
U.S. Pat. No. 6,327,245, “Automatic channel switching for jamming avoidance in burst-mode packet data wireless communication networks,” issued to Satyanarayana, et al. on Dec. 4, 2001, relates to the field of wireless networks in which a large number of nodes communicate with a central computer. The invention relates more particularly to avoiding jamming in such a system. The invention uses a single channel of communication.
U.S. Pat. No. 6,278,878, “Mobile communications system with portable terminal for facilitating channel switching,” issued to Noda on Aug. 21, 2001, describes a mobile communications system. A portable terminal can be used continuously in the mobile system without substantially terminating a communication session even when the communication with the mobile terminal is transferred from one base station to another as the terminal moves around.
U.S. Pat. No. 6,163,526, “Transmission system for switching connection from a working channel line to a protection channel line while avoiding instantaneous cutoff upon failure,” issued to Egoshi on Dec. 19, 2000, relates to a transmission system with multiple terminals linked by a working channel line and a protection channel line in a redundant structure wherein a connection is switched from the working channel line to the protection channel line while avoiding instantaneous cut off when the working channel line has failed. That system does not consider the possibility that even if there is no failure, it may be desired to switch from a working channel to the protection channel.
U.S. Pat. No. 5,995,807, “Method of switching a channel from a first propagation path to a second propagation path,” issued to Magnier, et al. on Nov. 30, 1999, describes a satellite telecommunications network for mobile stations. The network operates in a “switched diversity” mode in which a call set up between a first station, e.g., a base station, and a second station, e.g., a mobile terminal, can be transmitted over either one of two propagation paths, i.e., via one of two distinct satellites based on the measurement of a value representative of signal-to-noise ratio for each of said propagation paths, namely the current path and a next path.
U.S. Pat. No. 5,970,050, “Allocating communication traffic,” issued to Johnson on Oct. 19, 1999, describes a method for selecting one of a number of possible routes through a communications network from a first node to a second node. The method includes defining a relationship between a range of costs for routes and a traffic density for routes. The relationship is represented by a curve with at least one point of inflection. The method monitors and uses traffic density for each of the possible routes to establish the cost of each the possible route in accordance with the relationship. One of the possible routes is selected in dependence on the cost of each possible route as established by said relationship.
U.S. Pat. No. 5,828,655, “Hybrid access system with quality-based channel switching,” issued to Moura, et al. on Oct. 27, 1998, describes an asymmetric network communication system for use in a client-server environment having independent forward and return channels operating at different speeds and/or under different protocols on the same or different communication media to provide efficient utilization of shared resources. A network manager, such as a hybrid access system, effects transmission of packetized data on a forward (downstream) channel from a host server to multiple client devices coupled with a shared downstream media while simultaneously providing selectable multiple lower speeds of operation on shared or dedicated return (upstream) channels from the client devices to the host server depending on bandwidth availability, bandwidth demand, service level authorization, etc. for the return channel. Forward and return channels may be located on the same or different communication medium including a CATV network, direct broadcast satellite network, television or radio RF broadcast network, wireless or mobile cellular facilities or the like. The return channel may reside on a PSTN either directly coupled with the host server or connected with the network manager for subsequent transmission to the host server. The network manager handles or controls the forward and return communication to establish interactive full-duplex real-time network sessions between the host and a selected client device. The network manager switches upstream channel assignment based on quality of signals transmitted to the host. The system effects changes in the upstream transmitted power based on sensed conditions.
In U.S. patent application Ser. No. 09/862,899, “Method and system for assigning circuits to a new service request in a communications network,” filed on May 22, 2001 by Sahinoglu and Porikli, a method for admission decision of application service request to a network is described. It does not involve channel management after a service request is granted and placed on an available channel.
In general, the primary drawback of using the prior art methods is that other networks and other paths may, at a later time, better satisfy the objective function after the network and path have initially been selected. In that case, the selected path is no longer the optimal path. Based on prior art methods, there is no way to exploite the availability of multiple networks in an optimal way.
Many elements are known for building an infrastructure to generate, transmit and receive multimedia content over networks, such as the one shown in FIG. 1. For example, standards such as MPEG-2 and MPEG-4 play an important role in the efficient broadcast and distribution of audio and video content, see ISO/IEC 13818:1995, “Information Technology—Generic Coding of Moving Pictures and Associated Audio,” and ISO/IEC 14496:1999, “Information Technology—Coding of Audio-Visual Objects,” respectively. For transport over IP networks, there exist a variety of specifications defined by the IETF, see for example, “RTP: A Transport Protocol for Real Time Applications,” RFC 1889, January 1996 by Schulzrinne, et al., and “RTP Payload Format for MPEG-4 Audio/Visual Streams,” RFC 3016, November 2000 by Kikuchi, et al. Furthermore, for the search and retrieval of multimedia contents, MPEG-7 provides a standardized set of descriptors and descriptions schemes, see ISO/IEC 15938:2001, “Information Technology—Multimedia Content Description Interface.”
However, currently there is no standard that describes how these elements, either in existence or under development, relate to each other. The primary aim of the emerging MPEG-21 standard, officially referred to as ISO/IEC 21000, “Information Technology—Multimedia Framework,” is to describe how these relate to each other. It is expected that the various specifications that exist, or will be developed, will be integrated into a multimedia framework through collaboration between MPEG and other standardization bodies. The overall vision for MPEG-21 is to define a multimedia framework to enable transparent and augmented use of multimedia resources across a wide range of networks and devices.
Within the MPEG-21 framework, the fundamental unit of transaction is referred to as a “digital item.” A digital item is defined as a structured digital object with a standard representation and identification. The digital item includes resources (content) and associated descriptors The resources can include individual multimedia assets, such as MPEG videos, MP3 audio files. The descriptors include descriptive information about the internals of the resources, such as content identification and content-based descriptors, e.g., an MPEG-7 description. The proposed framework currently does not consider external descriptions, such as network condition, terminal characteristics, and user preferences.
MPEG-21 has recently developed a Digital Item Declaration (DID), Part 2 of ISO/IEC 21000, which is scheduled to become an international standard in May 2002. The purpose of the DID is to declare the make-up and structure of a digital item. An XML-based Digital Item Language Declaration (DIDL) has been developed. The DIDL is a generic structure to provide hierarchical and flexible meta-data expression, as well as re-usable and configurable elements. To enable an interoperable framework and support various applications, it is important that these descriptors be specified in a standardized way.
It is desired to provide descriptors that can also be used for optimal network and path selection. Furthermore, it is desired that the selection can change dynamically while terminals actively transmit and receive resources within any available network.